Positioning system

ABSTRACT

A positioning system is provided having a first signal source for originating synchronous signals, and a second signal source for originating a signal which is not synchronous with the signal from the first signal source. The system determines, based on a signal propagation time and signal propagation speed from the first or second signal source, the distance to this signal source so as to determine a position of a receiving point.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. Ser. No. 10/780,288 filed Feb.17, 2004, now U.S. Pat. No. 7,277,050 B2, claiming priority to JapaneseApplication No. 2003-054021 filed Feb. 6, 2004, all of which are herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a positioning system for use in GPS(Global Positioning Systems) assisted with mobile telephone networks forpositioning.

2. Description of the Related Art

Global positioning systems, or GPS, have been available. In GPS, signalssent from satellites are received to determine the distance to thesatellites to determine the position of the receiving point. In GPS,therefore, it is necessary to determine the position and time at whichthe satellites sent the signals. Satellite position information is sentfrom the satellites as almanac and ephemeris information, and can beacquired by picking up the signal from the satellites; however, it takesabout 15 minutes to receive all of the information. Since it isdifficult to supply accurate time information, generally, signals fromfour satellites are received to determine the position and time bysolving simultaneous equations with four unknowns, that is,three-dimensional position coordinates and time. In the related art,there has been a network-assisted GPS in which information necessary forpositioning, such as satellite position information and timeinformation, is obtained not via satellite signals but via informationin another way, such as a mobile telephone network, so as to greatlyimprove the positioning time and accuracy. Network-assisted GPSpositioning of WCDMA mobile phones has been standardized by the 3GPP(Third Generation Partnership Project) (see 3GPP Specification TS25.305V5.4.0).

In GPS, it is necessary to receive at least four satellite signals inorder to detect the three coordinates of position, i.e., latitude,longitude, and altitude, and the time, or to receive at least threesatellite signals, assuming that the altitude is ground level, in orderto detect the two coordinates of position, i.e., latitude and longitude,and the time. In bad visibility conditions for satellites, such asindoors or between buildings in cities, a required number of satellitesignals are not necessarily receivable. In order to overcome such asituation, a positioning technology in which radio signals fromtelephone-network base stations are used as satellite signals is known,and is standardized as OTDOA (Observed Time Difference Of Arrival)positioning technology, as shown in 3GPP Specification TS25.305 V5.4.0.FIG. 3 is a diagram showing the principle of a typical network-assistedGPS specified in 3GPP Specification TS25.305 V5.4.0. An SAS (Stand AloneServing Mobile Location Center) 12 receives GPS satellite signals toobtain almanac and ephemeris data necessary for detecting the position.The position of the SAS 12 is known, and the SAS 12 can further generatedata for correcting positioning errors from the difference between theknown position and the positioning result from the GPS signals. In somecases, the SAS 12 also provides a portion of the SMLC (Serving LocationCenter) functionality, which should be performed by an RNC (RadioNetwork Controller) 13 a. The RNC 13 a controls a base station 15 a toperform sequence control or radio resource management necessary forpositioning. The RNC 13 a specifies necessary assistance data from theSAS 12 based on positioning capabilities of the UE (User Equipment) tobe measured, and sends it to a UE 16 via the base station 15 a accordingto the positioning sequence. The timing necessary for UE positioning canbe determined using a pilot signal or the like sent from the basestation 15 a. In WCDMA, base stations and GPS satellites are notgenerally synchronous, and an LMU (Location Measurement Unit) installedin each base station measures the deviation from the GPS time. There aretwo types of LMUs, that is, type A for connection with the base stationby air, and type B for connection with the base station via a line.

Therefore, in such a typical network-assisted GPS using WCDMA mobiletelephone networks, a device (LMU) for measuring a time differencebetween a signal sent from a radio-access-network base station and asignal sent from a GPS satellite, which have no synchronous relationtherebetween, is essential in each base station.

Typically, in OTDOA technology, since signals from base stations are notsynchronous, the timing difference between the base stations must bemeasured by some method. Thus, an LMU is also required for each basestation in order to detect the timing difference of signals between thebase stations.

It is an object of the present invention for the base station to providea low-cost and high-reliability positioning system capable of preciselyproviding time to the positioning target UE and of OTDOA positioning inasynchronous WCDMA mobile telephone networks without installing an LMUin each base station.

It is another object of the present invention to provide a positioningsystem capable of short-time and high-accuracy positioning without anLMU.

SUMMARY

A positioning system of the present invention having one or a pluralityof first signal sources (GPS satellites) for originating synchronoussignals, and one or a plurality of second signal sources (basestations), for originating signals which are not synchronous with thesignals from the first signal sources, for originating a signal, for,based on a signal propagation time and signal propagation speed from thesignal source, and determining the distance to the signal source basedon a signal propagation time and a signal propagation speed from thesignal source so as to determine a position of a receiving pointincludes a measurement device (a mobile terminal in good conditions) forreceiving only the signal from the first signal source to determine areceiving position P (P is a vector quantity indicating the positioncoordinates) and time and for, based on the time, measuring a receivingtime T_(R) of a predetermined event of the signal from the second signalsource, a control device for determining a signal propagation time tbetween the measurement device and the second signal source bycalculating a relative distance |P-Q| between the measurement device andthe second signal source based on the receiving position P measured bythe measurement device and a position Q (vector quantity) of the secondsignal source and by dividing the resulting distance by the signalpropagation speed, and for determining a time T_(r) at which the secondsignal source originates the predetermined event by solving T_(R)−t, apositioning terminal having a receiving device for receiving the signalsfrom the first and second signal sources, and a communication device forperforming communication between the control device and the positioningterminal, wherein the positioning terminal uses the time T_(T) as areference to receive the signal from the first signal source forpositioning.

With this structure, the transmission timing of base-station signals isdetermined using a mobile terminal in good conditions, and the time isreported to the positioning target mobile terminal. This enables thepositioning target mobile terminal to know the accurate time without anLMU for each base station, thus achieving an advantage that thepositioning time can be reduced. No LMU is required, thus achievinganother advantage that the system construction cost can be reduced.

Since the positioning target mobile terminal measures a receiving timeof a predetermined signal from a base station, the distance from thepositioning target mobile terminal to the base station can be determinedbased on the obtained value and the time T_(T) determined by measurementof a mobile terminal in good conditions, thus achieving an advantagethat the location can be determined even in case a required number ofGPS satellites are invisible (e.g., unavailable due to weather,buildings, or the like).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a positioning system according to the presentinvention.

FIG. 2 is a block diagram of an UE for use in the positioning systemaccording to the present invention.

FIG. 3 is a diagram of a positioning system in a WCDMA mobile telephonesystem of the related art.

DETAILED DESCRIPTION

An embodiment of the present invention is described hereinbelow withreference to the drawings.

Embodiment 1

FIG. 1 is a diagram showing the main portion of a positioning systemaccording to the present invention. A reference station 8 receives GPSsatellite signals to obtain almanac and ephemeris data necessary forpositioning.

The position of the reference station 8 is known, and positioningcorrection data is generated by comparing this position and thepositioning result obtained from the GPS signals. The obtained data isstored in an SAS 7. A UEa 3 is a terminal which knows the approximateposition or time from the previous location data or which is in goodconditions where signals from a sufficient number of satellites forpositioning can be successfully picked up. An RNC 6 provides the SMLCfunctionality, and performs resource management or sequence controlnecessary for positioning. A UEb 4 is a target terminal for positioning.As shown in FIG. 2, each UE includes a GPS receiver 9 for receiving GPSsignals, and a WCDMA baseband processor 10 a for operating as a mobilephone.

The UEa 3 is a mobile terminal which allows its internal clock to becalibrated by a GPS time coordinated with an atomic clock, which isobtained from the previous positioning result, so as to know theaccurate time, or which receives radio waves of satellites 1 a, 1 b, 1c, and 1 d with sufficient signal strengths for stand-alone positioningif it does not know the accurate time. The RNC 6 regularly sendsinquiries to the UEa 3 via a BSa (base station) 2 a about the currentposition P and a GPS time T_(R) at which a specific event of the signalsent from the BSa 2 a is received, and calculates a GPS time T_(T) atwhich the BSa 2 a sent the specific event of the signal based on theresult. It is desirable that the specific event generated from a basestation be, for example, the transmission of a frame boundary or aspecific system frame number (for example, system frame No. 0) of apilot signal sent from a base station. In GPS, one-bit information issent for every 20 milliseconds; whereas, a WCDMA frame is set to 10milliseconds, thus facilitating calculation. Since every UE in a cellreceives a pilot signal and knows the frame timing, no special signal isadditionally required for positioning. The frame timing and/or thesystem frame number are passed from the WCDMA baseband processor 10 tothe GPS receiver 9 shown in FIG. 2.

Calculation of the time T_(T) from the time T_(R) is carried out in thefollowing way. The position Q of the BSa 2 a is known. The calculationcan be performed by solving the following relation equation:T _(T) =T _(R) −|P−Q|/c  (Eq. 1)

where c indicates the velocity of light, and |P-Q| indicates thedistance between P and Q. The time determined by the following equationindicates the time necessary for a radio wave to propagate from the BSa2 a to the UEa 3:t=|P−Q|/c  (Eq. 2)

Even if the UEa 3 is in good conditions, it requires more than tenminutes to obtain all almanac data and ephemeris data necessary forpositioning from satellites, and this is not practical. In general, theassistance data stored in the SAS 7 is obtained via the RNC 6 for use.

Every UE retrieves base-station signals when it is powered on todetermine which cell the UE is currently present in, and reports theresult to the RNC 6. The RNC 6 therefore has a list of all UEs in eachcell. The RNC 6 regularly sends inquiries for P and TR to the UEs ingood conditions based on the list so that T_(T) is constantly updated.Alternatively, a UE in good conditions may voluntarily report P andT_(R) regularly. Usually, a plurality of UEs, not only one UE, are ingood conditions, and the RNC 6 can use the reports from these terminalsto very precisely determine T_(T) using the least square method or thelike.

The UEb 4 is a terminal in bad conditions, such as indoors or betweenbuildings. In such conditions, high-sensitivity positioning can berealized by performing many calculations using satellite signals.However, unless the accurate time is known and the time when thecalculation starts is limited to some extent, it takes a very long timeuntil the signals are detectable. In this situation, positioning isimpossible in effect. The UEb 4 is able to calculate approximate timefrom the pilot signal from the BSa 2 a and T_(T) determined by the RNC6. The receiving time T at which the UEb 4 received the specific framecan be given by the following equation:T=T _(T) +n×10 ms+T _(p)  (Eq. 3)

where n denotes the number of frames sent from the BSa 2 a after T_(T)was observed until the UEb 4 receives this frame, and T_(p) indicatesthe signal propagation time from the BSa 2 a to the UEb 4. One frameperiod (10 ms) is controlled within ±0.05 ppm by the 3GPP standard, andthe error is small if T_(T) is updated frequently to some extent. T_(P)cannot be identified, and is used as it is.

The UEb 4 limits a search window of the satellite signals based on theassistance data supplied from the SAS 7 via the RNC 6 and T to detectthe signals for positioning.

The UEb 4 can receive three satellite signals and a base-station signalto obtain four simultaneous equations with unknowns, that is, thethree-dimensional position of the UEb 4 and the time, and can know itsposition.

The UEb 4 can also receive two satellite signals and a base-stationsignal to obtain four simultaneous equations with unknowns, that is, thetwo-dimensional position of the UEb 4 and the time, and can know itsposition.

The UEb 4 can also receive two satellite signals and two base-stationsignals to obtain four simultaneous equations with unknowns, that is,the three-dimensional position of the UEb 4 and the time, and can knowits position.

Likewise, if the sum of the received satellite and base-station signalsis four, the UEb 4 can obtain four simultaneous equations with unknowns,that is, the three-dimensional position of the UEb 4 and the time, toknow its position. If the sum of the received satellite and base-stationsignals is three, the UEb 4 can know the two-dimensional position andthe time.

A base-station signal is not necessarily used as a reference, but, forexample, a signal, such as a synchronous signal of television-stationradio waves, may be used as a reference. This is advantageousparticularly for the third generation multimedia-enhanced mobileterminals with a built-in TV receiver, which is one feature of thirdgeneration mobile phones.

Advantages

According to the present invention, the timing between base-stationsignals is measured by a mobile terminal. Therefore, in an asynchronousmobile-telephone-network system, base stations can report an accuratetime to a positioning terminal via base-station signals without an LMU.The positioning terminal can use the time to realize short-time andhigh-accuracy positioning.

According to the present invention, furthermore, the timing betweenbase-station signals is measured by a mobile terminal without using anLMU to determine the phases of the base-station signals. Thebase-station signals and GPS satellites can be used for positioning evenin case a required number of GPS signals are not receivable.

1. A positioning system for determining a position of a positioningterminal, the system including a plurality of first signal sources eachemitting a respective first signal, and one or more second signalsources each emitting a respective second signal, the first signalsbeing synchronous with a reference time and the second signals beingnon-synchronous with the first signals, for, based on a signalpropagation time and signal propagation speed of at least one of thefirst and second signal sources determining a position of thepositioning terminal, said positioning system comprising: a measurementdevice associated with each second signal source for receiving the firstsignals from the first signal sources to determine a position P of themeasurement device and a time of measurement when the measurement devicereceives the first signals and for, based on the time of measurement,measuring a receiving time (TR), based on the reference time, of apredetermined event of the second signals; a control device fordetermining a signal propagation time (t) between the measurement deviceand its associated second signal source by calculating a relativedistance |P-Q| between the measurement device and its associated secondsignal source based on the position P measured by the measurement deviceand a position Q of the second signal source and by dividing theresulting distance by the signal propagation speed, and for determininga time (TT), based on the reference time, at which the second signalsource originates the predetermined event by solving TR-t; thepositioning terminal including a receiving device for receiving fromamong the signals from the first and second signal sources; and acommunication device for communicating between the control device andthe positioning terminal, wherein the communication device communicatesthe time TT to the positioning terminal, and wherein the positioningterminal receives the time TT from the communication device and uses thetime TT to receive from among the first and second signals fordetermining the position of the positioning terminal.
 2. The positioningsystem according to claim 1, wherein the first signal sources furthercomprise GPS satellites.
 3. The positioning system according to claim 1,wherein the second signal sources further comprise base stations of amobile communication network.
 4. The positioning system according toclaim 1, wherein the measurement device further comprises a mobileterminal in good conditions, wherein the position P of the measurementdevice can be determined without accurate time information, and measuresP and TR to voluntarily report the measured P and TR to the controldevice in the same mobile communication network.
 5. The positioningsystem according to claim 1, wherein the measurement device furthercomprises a mobile terminal in good conditions, where the position P ofthe measurement device can be determined without accurate timeinformation, and measures P and TR according to a request from thecontrol device in the same network to report the measured P and TR tothe control device.
 6. A positioning terminal for determining a positionof the positioning terminal, the positioning terminal including areceiving device for receiving signals from a plurality of first signalsources each emitting a respective first signal and one or more secondsignal sources each emitting a respective second signal, the firstsignals being synchronous with a reference time and the second signalsbeing non-synchronous with the first signals, for, based on a signalpropagation time and signal propagation speed of at least one of thefirst and second sources determining a position of the positioningterminal, said positioning terminal comprising: a calculation device forcalculating TT=TR-|P-Q|/c; wherein the P is a position of a measurementdevice when the measurement device received the first signals from thefirst signal sources; the Q is a position of the one second signalsource; the |P-Q| is a relative distance between the measurement deviceand the one second source; the c is a signal propagation speed; the TRis a receiving time, based on the reference time, when the measurementdevice received a predetermined event of the second signals at theposition P; wherein the positioning terminal uses the time TT to receivethe signals from the first signal sources; wherein the positioningterminal receives from among the first and second signals fordetermining the position of the positioning terminal.
 7. The positioningterminal according to claim 6, wherein the first signal sources furthercomprise GPS satellites.
 8. The positioning terminal according to claim6, wherein the second signal sources further comprise base stations of amobile communication network.
 9. The positioning terminal according toclaim 6: wherein the measurement device further comprises a mobileterminal in good conditions; wherein the position P of the measurementdevice can be determined without accurate time information; wherein themeasurement device measures P and TR; and wherein the measurement devicevoluntarily reports the measured P and TR to the control device in thesame mobile communication network.
 10. The positioning terminalaccording to claim 6, wherein the measurement device further comprises amobile terminal in good conditions, where the position P of themeasurement device can be determined without accurate time information,and measures P and TR according to a request from the control device inthe same network to report the measured P and TR to the control device.11. The positioning terminal according to claim 6, wherein the secondsignal sources further comprise television broadcast stations.